ASK THE EXPERTS: Septic System Methane

Greetings! I’ve recently moved to a new house (I constructed it) that has a septic system. The thought has occurred to me that my septic system more than likely produces methane gas. As a result, I’ve been wondering if someone has developed some sort of a septic system methane digester — something that collects the gas and then compresses it so it can be stored and used. Thanks for any suggestions.

Guy Palmer, Lagunitas, California

Hello Guy, Folks frequently ask if the methane gas produced by a septic system can be harnessed. The short answer is no. The reason is that the design of a septic system does not foster the conditions that anaerobic organisms require in order to produce a significant amount of gas.

A septic tank is similar to a stagnant pond in your backyard. It will produce a tiny amount of methane gas, but not enough to be of practical use. Anaerobic organisms require three conditions to produce gas effectively:

A constant temperature between 95 and 100°F (35 and 38°C). Gas is produced at lower temperatures, but only in very small amounts over an extended period of time.

The exclusion of oxygen. A septic tank is not designed to keep out oxygen. Granted, some oxygen is excluded by virtue of the water in which the organic matter is transported, but a septic tank is not a sealed system.

A gentle mixing action. The bacteria that produce methane either have to be transported to their nourishment or their nourishment has to be taken to them. Gentle motion accomplishes this.

Comments (4)

Last time I checked, Methane Digester Septic Systems are used by some 100 million PLUS Chinese in the PRC, and they've been using them for DECADES........is this not the same thing as the original question asked?

It is very to important not to pour chemicals such as chlorine bleach products into your septic system. This can kill entire cultures of the bacteria micro-organisms that is mentioned in this article. It would completely disrupt the Septic System an cause it to be inactive.

we have a pumped system, what about collecting the methane out of the primary settling tank? It has less water and could more easily be sealed.
Also , I could imagine a simple thermosiphon tube to provide enough heat.
Maybe similar concentric tubes in the tank might provide enough circulation.

We just need enough gas to provide a back-up for our back=up generator, if power is out more than a week.